At traffic light warning system, with the red light indicating shootings going on outside, was set up by a Mexican church following widespread violence in the area.
St Teresa of Avila Church in Monterrey, which is one of Mexico's wealthiest cities, has adopted the system after a spate of shootouts and armed robberies beset the city, the Daily Mail reports.
During mass, a green light is activated from the top of a side door of the church, which means there is no presence of danger on the streets outside, the paper added.
As another security measure, the church has constructed a concrete wall in front of its main facade.
Posters and notices of missing or kidnapped people are hung inside the church, the paper added.